Question

Let $V_s$ be the speed of the source emitting sound waves, $n$ the actual frequency of the source of sound, $V$ the speed of the sound in the medium and $n_1$ the frequency of sound waves as perceived by a stationary observer to whom the source of sound is approaching. The formula for calculating $n_1$ is :

• A. $n_1=n(1-V_s/V)$
• B. $n_1=n\left(\frac{V}{V-V_s}\right)$
• C. $n_1=n/(1+V_s/V)$
• D. $n_1=n$

Answer 1

The correct option is B $n_1=n\left(\frac{V}{V-V_s}\right)$

The formula for calculating apparent frequency $n_1$ due to Doppler effect is:

$n_1=n\left(\frac{V-V_o}{V-V_s}\right)$

where $n$ is the frequency of sound waves

$V$ is the speed of sound in the medium

$V_o$ is the speed of the observer

$V_s$ is the speed of the source

Here $V_o=0$ as observer is stationary. Hence option (b)